共查询到20条相似文献,搜索用时 296 毫秒
1.
微通道中液氮的流动沸腾——换热特性分析 总被引:3,自引:0,他引:3
对微通道中液氮流动沸腾换热特性进行试验研究和分析。给出典型的沸腾曲线,分析壁温、干度和换热系数沿微通道管程的变化规律,考察热流密度、质量流量和压力对流动沸腾换热的影响。将126个试验数据点与四个换热关联式比较,并对微通道中流动沸腾换热机理进行分析。结果表明,在多数情况下干度和热流密度对沸腾换热系数的影响较小,换热系数主要决定于质量流量和压力,随两者增加而增加,换热以对流蒸发为主导机理。KLIMENKO关联式预测效果最好,TRAN微通道关联式次之,对常规管道得到广泛使用的CHEN关联式和SHAH关联式都远远高估了试验值。基于两相流压降和换热特性分析,推知微通道中的两相流流型不同于常规管道:在低干度情况下,流型以弥散泡状流为主;而在高干度情况下,流型以由雾状汽芯和不规则液膜组成的环状流为主。 相似文献
2.
3.
4.
5.
6.
高速列车制动时,制动盘摩擦表面的温度场直接影响制动盘表面磨损、相变、热裂纹及其使用寿命。以某型高速列车基础制动装置现役锻钢制动盘为研究对象,建立热载荷模型:考虑制动闸片几何形状和分布对热流密度的影响,建立了基于微元法的摩擦面热流密度计算模型;由于热辐射计算的非线性求解特性,将热辐射系数折算成等效对流换热系数,建立了对流换热模型与辐射换热模型相结合的综合换热模型。考虑到制动盘面和散热筋几何截面的突变性,建立了由盘面和散热筋六面体网格与接触部位过渡网格构成的制动盘热分析有限元模型。对高速列车在200km/h速度下紧急制动时制动盘瞬态温度场进行仿真分析。得到制动盘温度分布规律和温度变化曲线,为制动盘选材及结构优化提供相应理论参考。 相似文献
7.
《压力容器》2019,(12)
随着科技的发展,微电子设备的散热量越来越大,传统换热器将难以满足其散热需求。微通道散热是一种新型的高效换热技术,其结构紧凑、换热性能突出、运行安全可靠的特点引起国内外学术界和工业界的广泛关注。试验技术存在对换热装置加工工艺和测量仪器精度的高要求,成本高、准备周期长;数值模拟技术成本低、计算周期短,探索微通道内单相和气液两相流动换热特性更为便捷,其优势也日益突显。详细介绍了针对微通道换热器的传热流动数值模拟研究方法,对比分析了包含LBM模拟方法和VOF气液两相流模型在内的典型数值方法,并总结了数值模拟在微通道单相换热特性、气液两相换热特性和临界热流密度方面的研究进展。 相似文献
8.
9.
10.
11.
12.
13.
T. Nguyen M. Liu L. C. Zhang 《The International Journal of Advanced Manufacturing Technology》2014,73(1-4):341-352
This paper investigates the cooling effect when using an air jet at sub-zero temperature of ?15 °C in the plunge grinding of a cylindrical component made of high strength steel EN 26. A three-dimensional finite element heat transfer model with a moving heat source was developed to reveal the complexity of the heat transfer mechanism involved. It was found that the use of cold air does not significantly reduce the temperature rise in grinding and that the cooling effectiveness is mainly limited by the following facts: (a) the air jet is difficult to penetrate into the grinding zone, (b) the heat transfer coefficient provided by an air jet is small and (c) cooling is limited by the time which the rotating workpiece surface can be exposed to the jet impingement. The study also showed that the present modelling method can be used as a first tool to assess the feasibility of a new cooling medium for grinding operations. 相似文献
14.
15.
新型单圆锥体热沉单孔射流散热数值模拟* 总被引:1,自引:1,他引:0
射流冷却是高热流密度换热的有效方法之一,其热沉形状是影响换热的关键因素。提出一种新型圆锥体热沉,应用RNG k-ε 湍流模型,对新型单圆锥体热沉进行单孔水冷散热数值模拟,并进行试验验证。结果表明:单圆锥体热沉的散热效果明显强于常规平板热沉,前者的射流流体域比后者多一个转折区,转折区内存在二次冲击,使换热得到强化。雷诺数越大,圆锥体热沉散热性能越优异;在不同锥角(15°~60°)的单圆锥体热沉传热模拟中,当锥角在45°左右时,热沉表面的平均努塞尔数
数最高;圆锥体底面直径d 1和射流孔直径d 比值在1~3范围内,
数在比值为2.5左右达到最大值;射流高度H 与射流孔直径d 比值在5左右时,
数趋于最大。 相似文献
16.
《风机技术》2021,(1)
The flame temperature in the combustor of a gas turbine is usually as high as 2000 K, while the maximum temperature that can be endured by metal materials is less than 1200 K at present. Therefore, various protective and cooling measures are needed to ensure the operation life of the liner wall which wraps the flame. The lean premixed combustor can meet the increasingly stringent emission requirements, but it requires more air for premixed combustion and then less air for cooling and dilution. In order to obtain a better impingement jet cooling structure, this paper studied the impingement jet cooling structure with vertical circular holes of equal diameter under single outlet condition. The structural variables studied include the jet hole diameter D, the impinging distance Z, the jet hole length(jet plate thickness) t, and the jet-to-jet spacing X is ignored. Among them, X/D(the ratio of the jet-to-jet spacing to the jet diameter) is inversely correlated with the mass flow rate. Within the constant X/D being equal to 10, the influence of D, Z and t on the average heat transfer coefficient h of the target surface under same mass flow was determined by means of conjugate numerical heat transfer analysis and orthogonal test. The results show that Z has significant influence on h, D has moderate influence on h, and t has negligible influence on h. Further, by means of regression orthogonal test, the influence trend of parameters Z and D on h at X/D=10 was studied. The optimal values of Z and D within the research scope were found. 相似文献
17.
开槽砂轮缓进给深切磨削时工件表层温度场解析 总被引:2,自引:1,他引:2
采用热源法推导出开槽砂轮缓进给深切磨削时磨削弧区工件表层温度分布的理论解析式,并利用理论计算公式结合磨削实验完成了施加水射流冲击条件下工件表层温度场的推演计算,计算结果与实验结果基本吻合,证实了开槽砂轮辅以弧区定向高压水射流冲击强化换热的确具有良好的冷却效果。 相似文献
18.
小通道冷板作为一种有效的热控装置,已被广泛应用于高热流密度电子器件的热管理领域。文中以通道特征尺寸为2 mm 的串行、并行以及射流冲击/小通道混合液冷板为研究对象,旨在获取这3种结构形式冷板的极限散热能力和流动阻力损失的差异。研究结果表明:在相同冷却工质流量条件下,3种冷板的散热功率由大到小依次为串行通道、并行通道、射流冲击/小通道混合液冷板;串行通道冷板的板内阻力损失明显大于其余两者;在综合考虑压力损失和散热性能的基础上,根据不同热源热流密度条件选择合适的冷板结构,有望满足特定应用的需求。该研究可供小通道液冷板的设计和优化参考。 相似文献
19.